Problem 53 - Chemistry: Principles and Reactions

Question

Arrange the elements Sr, In, and Te in order of (a) decreasing atomic radius. (b) decreasing first ionization energy. (c) increasing electronegativity.

Step-by-Step Solution

Answer

Question: Arrange the elements Sr (Strontium), In (Indium), and Te (Tellurium) in order of (a) decreasing atomic radius, (b) decreasing first ionization energy, and (c) increasing electronegativity. Answer: (a) Decreasing atomic radius: Sr > In > Te, (b) Decreasing first ionization energy: Te > In > Sr, (c) Increasing electronegativity: Sr < In < Te.

Step 1: Find the periods and groups of the elements

Consult the periodic table to find that Sr is in period 5, group 2; In is in period 5, group 13; and Te is in period 5, group 16.

Step 2: Recall the trends for atomic radius

In the periodic table, atomic radius generally decreases as you move from left to right across a period and increases as you move down a group.

Step 3: Arrange the elements based on atomic radius

Sr, In, and Te are all in the same period (period 5). Sr is in group 2, In is in group 13, and Te is in group 16. Since atomic radius decreases as we move across a period from left to right, the order of decreasing atomic radius is Sr > In > Te.

Step 4: Recall the trends for ionization energy

In the periodic table, the ionization energy generally increases as you move from left to right across a period and decreases as you move down a group.

Step 5: Arrange the elements based on first ionization energy

Since all three elements are in the same period, we only need to compare their positions within the period. Moving from left to right, the order of decreasing first ionization energy is Te > In > Sr.

Step 6: Recall the trends for electronegativity

In the periodic table, electronegativity generally increases as you move from left to right across a period and decreases as you move down a group.

Step 7: Arrange the elements based on electronegativity

Since all three elements are in the same period, we only need to compare their positions within the period. Moving from left to right, the order of increasing electronegativity is Sr < In < Te. Final summary: (a) Decreasing atomic radius: Sr > In > Te (b) Decreasing first ionization energy: Te > In > Sr (c) Increasing electronegativity: Sr < In < Te

Key Concepts

Atomic Radius

The atomic radius is a measure of the size of an atom, typically the distance from the nucleus to the outermost shell of electrons. Periodic trends reveal that the atomic radius changes in predictable ways as you move around the periodic table.

• When you move from left to right across a period, the atomic radius decreases. This happens because electrons are added to the same energy level while protons are added to the nucleus, increasing the nuclear charge. As a result, the electrons are pulled closer, reducing the radius.
• Alternatively, when you move down a group, the atomic radius increases. This is due to the addition of electron shells where each level is further from the nucleus compared to the last, thus increasing the size of the atom.

In our example of strontium (Sr), indium (In), and tellurium (Te), all in period 5, the arrangement from largest to smallest atomic radius is Sr > In > Te, as these elements are ordered by decreasing radius to the right of a period.

Ionization Energy

Ionization energy refers to the energy required to remove an electron from a gaseous atom or ion. It can help us understand an element's reluctance to lose its electrons. The trends for ionization energy across the periodic table are clear:

• As you move from left to right across a period, ionization energy increases. This is due to the stronger attraction between the increased positive charge of the nucleus and the electrons, making it harder to remove an electron.
• Moving down a group, the ionization energy decreases. Here, electrons are further away from the nucleus, so it's easier to remove one despite the increased nuclear charge, due to the shielding effect of inner electrons.

In our context with Sr, In, and Te, all lying in the same period, the order of decreasing first ionization energy is Te > In > Sr. As anticipated, tellurium, being furthest to the right, retains its electrons more tightly compared to strontium on the far left.

Electronegativity

Electronegativity is an atom's tendency to attract and bond with electrons. This property also exhibits trends across the periodic table, reflecting the inherent electron affinity of elements.

• As you move across a period from left to right, electronegativity typically increases. Nuclei further to the right have more protons, attracting bonding electrons more effectively.
• Conversely, as you move down a group, electronegativity decreases, since the addition of electron shells places the bonding electrons further from the nucleus. The inner electrons also create a shielding effect, weakening the nucleus's pull on new electrons.

For the elements in question, Sr, In, and Te, which lie within the same period, the order of increasing electronegativity is Sr < In < Te. Tellurium again acquires the highest electronegativity, pulling electrons towards itself more effectively than strontium or indium.